WASHINGTON -- Defense Secretary Ash Carter acknowledged Thursday he used a personal email account to conduct some government business during his first months on the job.

In an interview with CBS during a trip to the Middle East, Carter called it "a mistake, and it's entirely my own." The same practice by former Secretary of State Hillary Clinton, now the front-runner for the Democratic presidential nomination, has drawn intense criticism and led to an FBI investigation into two emails that now are considered top secret.

Carter said he used his iPhone to send "administrative messages." He said none contained classified information, and all were backed up for record keeping on the Defense Department email system.